Required field raises "invalid literal for int() with base 10'' in admin

[beheh]

In the Django admin, when leaving a dropdown field with null=True but blank=False on the default selection of "---------", line 28 in the following code raises invalid literal for int() with base 10':

django-intenumfield/django_intenum/__init__.py

Lines 26 to 29 in 579a2b8

	def format_value(self, value):
	if value is not None:
	value = int(value)
	return super().format_value(value)

This is probably happening because the value is an empty string in this case, which should probably be treated like None in the affected function since an enum can't have a member with the empty string as name.